The principle for paging a User Equipment (UE) of the 3rd Generation Partnership Project (3GPP) protocol is that:
paging information of the UE is transmitted through a Paging Channel (PCH).
A Paging Indicator Channel (PICH) is defined, which carries Paging Indicator (PI) information of the UE. Thus, without demodulating the paging channel in real time, the UE can know whether it is paged currently by only monitoring information of a particular PI location of the PICH according to a specified period, and then decides whether to demodulate the PCH, thus achieving the purpose of saving power of the UE.
There are 288 bits per frame in the PICH for carrying Paging Indicators (PIs), and the number i.e., Np, of PIs which can be carried at the same time may be taken as 18, 36, 72 or 144. Np is obtained from a PICH mode information element of a COMMON TRANSPORT CHANNEL SETUP REQUEST message sent by a Radio Network Controller (RNC) to a base station (or a NodeB).
FIG. 1 is a diagram of a structure of a PCH frame sent by a RNC to a base station. Wherein, a PI-bitmap field includes Np bits, each bit corresponds to one PI, each PI corresponds to one user, and a bit string for indicting the value of the PI within a payload field in the PICH frame corresponding to each PI is referred to as a BitsGroup, and the number of bits occupied by the BitsGroup is 288/Np.
For example, when Np=144, a BitsGroup corresponding to each PI occupies 2 bits; and
for example, when Np=18, a BitsGroup corresponding to each PI occupies 16 bits.
The BitsGroup is used to carry the PIs. Take Np=18 as an example. Each BitsGroup includes 16 bits. If PI is 1, all bits in the BitsGroup corresponding to the PI are 1; and if PI is 0, all bits in the BitsGroup corresponding to the PI are 0.
According to the requirements of the 3GPP protocol, if there is a user paged at a location corresponding to a PI, the PI is set to 1, and all bits in the BitsGroup corresponding to the PI are 1; and there is no user paged at a location corresponding to a PI, the PI is set to 0, and all bits in the BitsGroup corresponding to the PI are 0.
Take Np=18 and PI bitmap=‘010010000000000000’ as an example. The contents transmitted by the PICH frame are shown in FIG. 2.
The 3GPP has the following problems with the current processing of the PICH:
According to the definition of the 3GPP, in the PICH frame, when there is no UE needed to be paged, the PI of a corresponding location of the UE is 0, the BitsGroup corresponding to the PI transmits all 0, and the transmission power of the BitsGroup is the same as that of a BitsGroup which transmits all 1 when there is paging.
Generally, in order to ensure a higher paging success rate, it needs to configure a higher PICH power. However, in fact, when there is no paging, a smaller power may be used, which allows PICH false detection with a certain probability.
Table one gives a common channel power configuration of commercial typical cell when Np=18.
TABLE ONEChannel typeNumberPowerDuty cycleConversion to WPCPICH133 dbm12.000PCCPCH1−3 db0.90.900PICH1−7 db0.960.382PSCH1−5 db0.10.063SSCH1−5 db0.10.063Total power (W): 3.408(Note:according to the requirements of the 3GPP protocol, for the downlink common channels, except that the PCIPCH uses an absolute power in units of dbm, powers of other channels are relative to the power of the PCPICH in units of db, similarly hereinafter)
According to the above typical common channel configuration, the power of the PICH occupies 11.3% of the no-load total power. In fact, if Np is greater than 18, the power of the PICH occupies a larger proportion of the total power.
In a commercial network, in most cases, the corresponding PIs in the PICH are 0, that is, there is no user paged. At this time, if the PICH frame continues to be transmitted at the PICH power configured according to the 3GPP protocol, it will result in a waste of power. The waste of the PICH power also increases downlink interference of the cell, deteriorates the pilot channel quality of the cell primary common pilot channel (for example, Echo), and influences the downlink coverage and the normal quality of service.